Conventionally, a fuel pump for supplying fuel to an engine body is directly connected to a valve system camshaft in the engine body, and driven.
However, when a high-pressure fuel pump is necessary, a driving force of a valve system camshaft may be deprived of by a fuel pump because the driving load of the fuel pump is large. In view of the above, in order to avoid lowering of a driving force of a valve system camshaft, there is proposed an idea, in which a drive shaft independent of the valve system camshaft and dedicatedly used for a high-pressure fuel pump is provided, a fuel pump is connected to the drive shaft, and the fuel pump is driven via the drive shaft for isolating the fuel pump from the valve system camshaft in terms of a structure.
Specifically, a flange portion is formed on an end portion of a cylinder block in the crankshaft direction to project from a surface of the end portion along the crankshaft direction in a direction orthogonal to the crankshaft direction. Further, a high-pressure fuel pump is mounted on one surface of the flange portion in a cantilever state. The high-pressure fuel pump includes a pump body, a pump housing surrounding the pump body, and a dedicated pump drive shaft which is rotatably supported on the pump housing. For instance, Japanese Unexamined Patent Publication No. 2007-16716 discloses, as a structure similar to the aforementioned structure, a configuration, in which a bulging portion is formed on a vehicle-front-side portion of a chain cover for covering a timing chain to bulge from the vehicle-front-side portion toward the vehicle front side, and a high-pressure fuel pump is fixed to one surface of the bulging portion in a cantilever state.
In the aforementioned structure, when a high-pressure fuel pump is disposed on the transmission side of a cylinder block, the offset amount of the high-pressure fuel pump from a crankshaft further increases in order to avoid interference between the high-pressure fuel pump and a transmission.
In the conventional mounting structure as described above, the following drawback may occur. Specifically, a high-pressure fuel pump, which is a heavy object, is mounted on a surface of a flange portion projecting from a surface of an engine in a cantilever state. This makes it difficult to sufficiently secure support rigidity of the fuel pump.
Further, positional precision of a pump drive shaft with respect to a cylinder block may not be sufficiently obtained due to a mounting error of a fuel pump with respect to a flange portion. As a result, tension of a timing chain may not be kept in an appropriate state, and a driving resistance of an engine may increase. This may deteriorate fuel efficiency.
There is an idea that the thickness of a flange portion is increased in the crankshaft direction in order to increase the rigidity of the flange portion. However, if the thickness of a flange portion is increased, the length of an intake manifold in the crankshaft direction may be limited. Therefore, there is a limit in increasing the rigidity of a flange portion by increasing the thickness of the flange portion.